The following abbreviations are used herein.
3GPP3rd Generation Partnership ProjectACKPositive acknowledgementBSWireless access point/base stationCACarrier AggregationCCComponent Carrier (i.e. PCell or SCell)CIFCarrier Indicator FieldDCIDownlink Control InformationDLDownlinkDRXDiscontinuous receptionDTXDiscontinuous transmissioneCAEnhanced Carrier AggregationeNB or eNodeBEvolved NodeBHARQHybrid Automatic Repeat RequestL1Layer 1 or Physical LayerL2Layer 2 or MAC/RLC layerLTELong Term EvolutionNACKNegative AcknowledgmentPCCPrimary Component Carrier (i.e. PCell)PDCCHPhysical Downlink Control ChannelPDSCHPhysical Downlink Shared ChannelPRBPhysical Resource BlockPUCCHPhysical Uplink Control ChannelPUSCHPhysical Uplink Shared ChannelRel′8 or r-8LTE Release 8Rel′ 10 or r-10LTE Release 10Rel′ 13 or r-13LTE Release 13RRCRadio Resource ControlRXReceiveSCCSecondary Component Carrier (i.e. SCell)SIBSystem Information BroadcastTPCTransmit Power ControlTXTransmitUCIUplink Control InformationUEUser EquipmentULUplinkUSSUE Specific Search Space
3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) wireless systems aim to provide enhanced services by means of higher data rates and lower latency with reduced cost. The first release of LTE wireless system (i.e. LTE Release 8) supports flexible bandwidths up to 20 MHz in the uplink (reverse link) and downlink (forward link). The later Release 10, which supports bandwidths larger than 20 MHz and up to 100 MHz, was standardized utilizing the concept of carrier aggregation (CA) to meet the requirements for ITU IMT-Advanced. IMT-Advanced, which stands for “International Mobile Telecommunications-Advanced”, are requirements issued by the International Telecommunication Union (ITU) for what is marketed as 4G mobile phone and Internet access services.
With CA, Release 10 and above UEs are able to aggregate up to five component carriers (CCs) to achieve total bandwidths greater than 20 MHz and as high as 100 MHz, as illustrated in FIG. 1. Backward compatibility is achieved by restricting the maximum bandwidth of one component carrier (CC) to 20 MHz with Release 8 structure such that legacy UEs observe each CC as a separate Release 8 carrier.
In Release 10 CA, the number of aggregated CCs and the bandwidth of each CC can be different for uplink (UL) and downlink (DL) providing symmetric or asymmetric configurations. Typically, in asymmetric configurations the number of DL CCs is larger than the number of UL CCs. A CA capable UE is initially configured with one UL/DL CC pair, called primary component carriers (PCC or PCell), on which it makes the initial random access. Depending on the UE capability and the network requirements, the network may configure additional CCs, called secondary component carriers (SCCs or SCells). Up to Release 12, the maximum number of SCells supported by a CA capable UE is four giving a total of five CCs including the PCell.
Additionally, in LTE, a hybrid automatic repeat request (HARQ) mechanism is employed in both uplink and downlink. For a scheduled downlink transmission to a UE, the UE attempts to receive and decode the data packet and feeds back an acknowledgement (i.e. positive: ACK or negative: NACK or DTX) to the eNodeB indicating whether the decoding was successful (ACK) or unsuccessful (NACK) or undetected. At an eNodeB, upon receiving a NACK corresponding to previously sent packet, the eNodeB may retransmit the non-decoded/erroneous/non-detected data packet. At a UE, transmission of acknowledgements for a received downlink data packet is done as a part of uplink control information (UCI)/layer 1 and layer 2 (L1/L2) control information, which are transmitted either on Physical Uplink Control Channel (PUCCH) or multiplexed onto uplink data transmission (if UL is granted in a subframe) on Physical Uplink Shared Channel (PUSCH). Up to Release 12 CA, PUCCH transmission is supported only on the primary uplink CC. This means there is a certain UE Category that is DL-CA capable (only) but non-UL-CA capable—i.e. UEs having multiple receivers (RX) but only a single transmitter (TX). According to LTE Release 10, the HARQ-ACK transmission for up to five DL CCs is done on one PUCCH on the PCell using PUCCH Format 3.
According to LTE Rel'10, when a UE is configured to use PUCCH Format 3 with CA enabled, the UE is further configured, via RRC signalling, with 4 PUCCH format 3 resources. On a DL subframe basis, the eNB dynamically informs the UE which resource (among the 4 configured PUCCH format 3 resources) is to be selected for mapping of the associated PUCCH carrying uplink control information (UCI) and associated transmit power. The eNB uses 2-bits of the Transmit Power Control (TPC) field in the PCell's DCI to dynamically signal the PUCCH power control command and 2-bits of the TPC field in SCell's DCI to dynamically signal the selected PUCCH resource index (the UE may assume the TPC command in all SCells DCI are the same). In this manner, the scheduler has the flexibility of allocating the same PUCCH resources set for multiple UEs via RRC while avoiding PUCCH collisions between those UEs by dynamically assigning them to different resources on a subframe basis.
Furthermore, in LTE, scheduling of a CC (in the form of downlink assignments/uplink grants) is done using downlink control information (DCI) transmitted on Physical Downlink Control Channel (PDCCH). In LTE Release 8, a UE only operates with one DL CC and one UL CC, and thus there is a clear association between the DL assignments/UL grants and the corresponding DL/UL CC. On the introduction of CA in Release 10, two modes of scheduling were introduced for handling multiple CCs and their association. The first mode of operation, known as self-scheduling, shown in FIG. 2, is a direct extension of the Release 8 concept, where a DL assignment/UL grant contained in a DCI transmitted on a CC is either valid for the DL CC itself or for the associated UL CC. The second mode of operation, known as cross-carrier scheduling, augments a DCI with a carrier indicator field (CIF) such that a DL assignment with CIF is valid for the DL CC indicated by that CIF, and UL grant with CIF is valid for the UL CC indicated by that CIF. In this manner, as illustrated in FIG. 3, PDCCH carrying DCI of one carrier can schedule PDSCH/PUSCH of the same DL carrier/associated UL carrier and one or more other DL carriers/their associated UL carriers, subject to the restriction that one CC can be scheduled by only one other CC and PCC cannot be cross-carrier scheduled.
Further, in Rel'10 LTE cross-carrier scheduling, when one CC schedules one or more other CCs, each scheduled CC has its own UE specific search space in the scheduling CC's control region (PDCCHs). As illustrated in FIG. 3, these UE specific search spaces may overlap with one another depending on the PDCCH capacity of the scheduling cell. The location of the each search space within the scheduling CC's control region is derived as a function of the CIF value which is same as the “servecellindex” of the scheduled CC (see Non Patent Literature 1).
Currently, 3GPP is working towards standardising enhanced carrier aggregation (eCA) to support aggregation on up to 32 component carriers in the downlink for upcoming Release 13. One identified requirement of this is to provide standardised support for aggregating 32 DL CCs with only one UL CC. This is for the UE Category with DL CA capability up to 32 CCs (32 RX) but no UL CA capability (1 TX) (see Non Patent Literature 2). In order to fulfil this requirement, the UE should be capable of reporting HARQ-ACK of up to 32 CCs simultaneously on PUCCH or PUSCHs on the primary UL carrier component. Clearly, the capacity of Release 10 standardized PUCCH format 3 is sufficient only for up to five CC's HARQ-ACK feedback, and therefore, a mechanism is required for transmitting/mapping a new PUCCH format with larger payload size spanning multiple PUCCH resources or PRB-pairs per UE. Additionally, in Rel'10 LTE, cross carrier scheduling is enabled with the use of a 3-bit CIF included in DCI formats for identifying scheduled SCells. Technically, 3-bits CIF can indicate up to 8 CCs, which is more than sufficient for the up to 5 CCs of Rel'10 CA. However, a 3-bit CIF is not sufficient to support cross carrier scheduling for carrier aggregation of up to 32 CCs in Release 13 with full flexibility—that requires at least 5-bits. However, extension of CIF to 5-bits is not preferred due to increased DCI overhead and specification rework.
Thus, there appears to be a need for a way to support efficient PUCCH resource allocation/collision handling and a mechanism to enhance flexible scheduling on up to 32 CCs per UE. Preferably this may be achieved while also achieving full backward compatibility with prior LTE's releases and also with the introduction of minimal rework through e.g. high layer signalling enhancement and operational procedure enhancement.
It is to be clearly understood that mere reference herein to any previous or existing apparatus, products, systems, methods, procedures, protocols, mechanisms, practices, publications (including the References and standard releases referred to herein) or any other information, or to any problems or issues, does not constitute an acknowledgement or admission that any of those things, whether individually or in any combination, formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.